Tag: Parkinson disease

A growth factor called Glial cell line-derived neurotrophic factor (GDNF) has the remarkable ability to supports the growth and survival of dopamine-using neurons. Dopamine-using neurons are the cells that die off in Parkinson’s disease (PD). Providing GDNF to dopamine-using neurons can help them survive , but getting GDNF genes into the central nervous system relies on invasive intracerebral injections in order to pass through the blood-brain barrier.

Typically, genes are placed into the central nervous system by means of genetically engineered viruses. Viruses, however, are often recognized by the immune system and are destroyed before they can deliver their genetic payload. Therefore, non-viral gene delivery that can pass through the blood-brain barrier is an attractive alternative, since it is non-invasive. Unfortunately, such a high-yield technique is not yet available.

A new study by workers in the laboratories of Hao-Li Liu from Chang Gung University and Chih-Kuang Yeh from National Tsing Hua University, Taiwan has utilized a novel, non-viral gene delivery system to deliver genes into the central nervous system.

In this study, Lui and Yeh and their research teams used tiny bubbles made from positively-charged molecules to carry genes across the blood brain barrier. These bubbles formed stable complexes with GDNF genes, and when the skulls of laboratory animals were exposed to focused ultrasound, the bubble-gene complexes permeated the blood brain barrier and induced local GDNF expression.

In fact, this technique outperformed intracerebral injection in terms of targeted GDNF delivery. The amount of GDNF expressed in these laboratory animals that received the GDNF gene/microbubbles + ultrasound protocol was significantly higher than those animals that had genes directly injected into their brains. Furthermore, these higher levels of GDNF genes increased the levels of neuroprotection from PD. Animals that had a form of PD and had received nonviral GDNF gene therapy showed reduced disease progression and restored behavioral function.

This interesting study explores the potential of using ultrasound-induced passage through the blood brain barrier to bring genes into the central nervous system. This noninvasive technique successfully delivered genes into the brain to delay the effects of, and possibly treat, a neurodegenerative disease.

This study was published in Scientific Reports6, Article number: 19579 (2016), doi:10.1038/srep19579.

Administering growth factors to the brains of patients with neurodegenerative diseases can prevent neurons from dying and maintain the structure of their brains. For example, a recently published clinical trial by Nagahara and others from the Department of Neuroscience and the University of California, San Diego examined 10 Alzheimer’s disease (AD) patients and showed that these patients responded to Nerve Growth Factor gene therapy. When they compared treated and nontreated sides of the brain in 3 patients who underwent gene transfer, expansion of cholinergic neurons was observed on the NGF-treated side. Both neurons exhibiting the typical pathology of AD and neurons free of such pathology expressed NGF, which indicates that degenerating cells can be infected with therapeutic genes. No adverse pathological effects related to NGF were observed. In the words of this study, “These findings indicate that neurons of the degenerating brain retain the ability to respond to growth factors with axonal sprouting, cell hypertrophy, and activation of functional markers. [Neuronal s]prouting induced by NGF persists for 10 years after gene transfer. Growth factor therapy appears safe over extended periods and merits continued testing as a means of treating neurodegenerative disorders.” See JAMA Neurol. 2015 Oct 1;72(10):1139-47.

Another study that also shows that the brains of AD patients can respond to growth factors comes from a paper by Ferreira and others from the Journal of Alzheimers Disease. These authors hail from the Karolinska Institutet, Stockholm, Sweden, and they implanted encapsulated NGF-delivery systems into the brains of AD patients. Six AD patients received the treatment during twelve months. These patients were classified as responders and non-responders according to their twelve-month change in the Mini-Mental State Examination (MMSE), which is a standard. In order to set a proper standard of MMSE decline and brain atrophy in AD patients, Ferreira and other examined 131 AD patients for longitudinal changes in MMSE and brain atrophy. When these results provided a baseline, the NGF-treated were then compared with these baseline data. Those patients who did not respond to the implanted NGF showed more brain atrophy, and neuronal degeneration as evidenced by higher CSF levels of T-tau and neurofilaments than responding patients. The responders showed better clinical status and less pathological levels of cerebrospinal fluid (CSF) Aβ1-42, and less brain shrinkage and better progression in the clinical variables and CSF biomarkers. In particular, two responders showed less brain shrinkage than what was normally experienced in the baseline data. From these experiments, Ferreira and others concluded that encapsulated biodelivery of NGF might have the potential to become a new treatment strategy for AD.

Now new, even simpler treatment strategy has been developed by a research team funded by the National Institute of Biomedical Imaging and Bioengineering for delivering gene therapy to the brains of AD patients. This team invented an eye drop cocktail that can deliver the gene for a growth factor called granulocyte colony stimulating factor (G-CSF) to the brain. They have tested these eye drops on mice with stroke-like injuries.

When treated with these eye drops, the mice experienced a significant reduction in shrinkage of the brain, neurological defects, and death. Ingeniously, this research group also devised a way to use Magnetic Imaging Systems to monitor how well the gene delivery worked. This one-two punch of an inexpensive and noninvasive delivery system combined with a monitoring technique that is equally noninvasive might have the ability to improve gene therapy studies in laboratory animals. Such a strategy might also be transferable to human patients. Imagine that acute brain injury might be treatable in the near future by emergency medical workers by means of eye drops that carry a therapeutic gene.

The growth factor G-CSF (granulocyte-colony stimulating factor) has more than proven itself in several animal studies. In model systems for stroke, AD, and Parkinson’s disease, G-CSF promotes neuronal survival and decreases inflammation (See McCollum M, et al., Mol Neurobiol. 2010 Jun;41(2-3):410-9; Frank T, et al., Brain. 2012 Jun;135(Pt 6):1914-25; Prakash A, Medhi B, Chopra K. Pharmacol Biochem Behav. 2013 Sep;110:46-57; Theoret JK, et al., Eur J Neurosci. 2015 Oct 16. doi: 10.1111/ejn.13105). Unfortunately, when G-CSF was when tested in a human trial in more than 400 stroke patients, it failed to improve neurological outcomes in stroke patients. Therefore, it is fair to say that the excitement this growth factor once generated is not what is used to be. A caveat with this clinical trial, however, is that G-CSF expression in the brains of these patients might have been rather poor in comparison to the expression achieved in mice. To properly establish the efficacy or lack of efficacy of gene therapies in human patients, scientists MUST convincingly determine that the gene is expressed in the target tissue of test subjects. This has been a perennial problem that has dogged many gene therapy trials.

Philip K. Liu, Ph.D., of the Martinos Center for Biomedical Imaging at Harvard Medical School, and his collaborators, H. Prentice and J. Wu of Florida Atlantic University, developed the novel MRI-based techniques for monitoring G-CSF treatment and the eye drop-based delivery system as well. MRI can efficiently confirm successful administration and expression of G-CSF in the brain after gene therapy delivery. This work was published in the July issue of the journal Gene Therapy.

“This new, rapid, non-invasive administration and evaluation of gene therapy has the potential to be successfully translated to humans,” says Richard Conroy, Ph.D., Director of the NIBIB Division of Applied Science and Technology. “The use of MRI to specifically image and verify gene expression, now gives us a clearer picture of how effective the gene therapy is. The dramatic reduction in brain atrophy in mice, if verified in humans, could lead to highly effective emergency treatments for stroke and other diseases that often cause brain damage such as heart attack.”

Liu’s motivation for this project was to develop a gene delivery method that was simple, and could rapidly and effectively deliver the genes to the brain. A simple gene delivery technique would obviate the need for highly trained staff and expensive, sophisticated equipment. They also sought to successfully demonstrate the efficacy of their technology in laboratory animals so that it could be translated to humans.

To test their system, they deprived mice of blood flow to their brains, and then administered a genetically-engineered adenovirus that had the G-CSF gene inserted into its genome. This particular adenovirus is known to be quite safe in humans and can also efficiently infect brain cells. The adenovirus was also safely and effectively administered through eye drops. The simplicity of the eye drops means that it is easy to give multiple gene therapy treatments. By delivering the G-CSF gene at multiple time points after the induced blockage, Liu and others found that the treated mice showed significant reductions in deaths, brain atrophy, and neurological deficits as measured by behavioral testing of these mice.

MRI examinations also confirmed that G-CSF was expressed in treated mouse brains. Liu and his group used an MRI contrast agent tethered to a segment of DNA that targets the G-CSF gene. This inventive strategy enabled MRI imaging of G-CSF gene expression in mouse brains. The brains of mice treated with the recombinant adenovirus showed significant expression of the G-CSF gene. Control mice treated with the same adenovirus carrying the contrast agent bound to a different piece of DNA produced no MRI signal in the brain.

Control mice that did not receive G-CSF in eye drops, MRI scan identified areas of the brain with reduced metabolic activity and shrinkage as a result of the stroke. Mice treated with the G-CSF gene therapy, however, kept their usual levels of metabolic activity and did not have any evidence of brain atrophy. On average, after a stroke, mouse brain striatum size decreased more than 3-fold, from 15 square millimeters in normal mice to less than 5 square millimeters. But in contrast, G-CSF-treated mice retained an average striatum volume of more than 13 square millimeters, which is close to normal brain volume.

“We are very excited about the potential of this system for eventual use in the clinic,” says Liu, “The eye drop administration allows us to do additional treatments with ease when necessary. The MRI allows us to track gene expression and treatment success over time. The fact that both methods are non-invasive increases the ability to develop, and successfully test gene therapy treatments in humans.”

Liu and his collaborators are now jumping through the multitudes of hoops to take this work to a clinical trial. They are trying to secure FDA approval for the use of the G-CSF gene therapy in human patients. Finally, they also need to invite collaborating with physicians to develop their clinical trial protocol.

Neurologist Ole Isacson and his Harvard Medical School team successfully implanted neurons made from a monkey’s own cells to treat Parkinson’s disease in those animals. The implanted neurons were watched for two years, and they proved to be both safe and effect in the treatment of Parkinson’s disease.

Induced pluripotent stem cells or iPSCs are made from mature, adult cells by means of a combination of genetic engineering and cell culture techniques. The cells resemble embryonic stem cells in many of their growth characteristics and gene expression patterns, but they are have several differences as well. One of the biggest differences between iPSCs and embryonic stem cells is that the reprogramming process that makes iPSCs places cells under stresses that increase the mutation rate and makes iPSCs, on average, more likely to cause tumors than embryonic stem cells. However, it is also clear that not all iPSC lines are the same and careful screen protocols that determine safe lines from less safe lines.

A distinct advantage of iPSCs over embryonic stem cells is that they have the same set of cell surface proteins as the patient from whom they were made, which makes them less likely to be rejected by the patient’s immune system. Even though some experiments had shown that cells derived from iPSCs can be rejected by the patient’s immune system, these experiments used poor-quality iPSC lines. High-quality iPSCs lines are much less likely to be rejected by the immune system. Therefore, using a patient’s own stem cells has distinct advantages as opposed to embryonic stem cells.

Isacson and his colleagues made patient-specific iPSCs from cynomolgus monkeys and used them to produce midbrain dopamine-making neurons – the kind that die off in patients with Parkinson’s disease – and used them to treat those same monkeys that suffered from Parkinson’s disease.

Such an experiment is potentially risky because even though differentiation of pluripotent stem cells into midbrain dopamine-making neurons is feasible, getting pure cultures of these cells that do not have any non-differentiated cells that can cause tumors is not all that easy to do. Fortunately, some advances in these techniques in the past few years have increased the ability of laboratories to not only produce large quantities of midbrain dopamine-making neurons, but screen them properly before transplantation.

In this experiment, Isacson and his team analyzed their implants for up to 2 years. The implanted animals were subjected to routine observations and tests, and in one animal, with the most successful protocol, they observed that lateral engraftment of CM-iPSCs on one side of the animal’s brain produced a gradual onset of functional motor improvement on the side opposite to the that of dopamine neuron transplantation, and increased motor activity. These implantation also did not require any immunosuppression and the implants caused to evidence of graft rejection. Postmortem analyses of these implanted animals revealed robust survival of midbrain-like dopaminergic neurons and extensive outgrowth into the tissue into which the cells were transplanted; the putamen, which is one of the “basal ganglia” that help control voluntary movements.

This remarkable proof-of-concept experiment supports further development of iPSC-derived cell transplantation for treatment of Parkinson’s Disease.